1. Field of the Invention
The present invention relates to the rebuilding of fuel injection pumps which have become inoperative due to excessive wear. In particular, the invention relates to the restoring of damaged surfaces on parts of the fuel distribution assembly of such pumps, i.e., head and rotor assemblies used in rotary distributor type diesel fuel injection pumps, as well as plunger and barrel assemblies of in-line diesel injection distributor pumps.
2. Description of Related Art
Distributor type fuel injection pumps are used to deliver fuel to the injectors of the respective cylinders of an engine in sequential order. An example of such a distributor type injection pump is the DPA type distributor pump manufactured by C.A.V. Limited, Acton, London, W.3, England. With reference to FIGS. 1A, 1B, fuel injection is effected in such a pump by a single element having twin opposed plungers located within a transverse bore in a central rotating rotor member which acts as a distributor and revolves in a stationary member known as the hydraulic head. The metering pump plungers are actuated by lobes on an internal cam ring. Fuel is accurately metered to the pumping element based upon a variable fuel pressure set by a transfer supply pump carried on an opposite end of the rotor from the plungers. The high pressure charges of fuel are distributed to the engine cylinders at the required timing intervals through ports in the rotor and hydraulic head. FIG. 1A shows the charging phase and FIG. 1B the actual pumping and distribution of the metered charge. As the rotor turns, a charging port in the rotor is aligned with the metering port in the hydraulic head and fuel metered by pressure flows into the central passage in the rotor and forces the plungers apart. The amount of plunger displacement is determined by the amount of fuel which can flow into the element while the ports are aligned. The inlet port closes as rotation continues and as the single distributor port in the rotor comes into alignment with one of the distributor ports in the hydraulic head, the plungers are forced inwards, generating high pressures which cause the fuel to pass to the injector.
Because the fuel is under high pressure (3,000-10,000 psi), the rotation of the rotor, and particles may be present within the fuel despite it being passed through a fuel filter, both the rotor and hydraulic head are subject to wear in the form of scoring, pitting, and/or chipping. Similar damage can occur if the rotor siezes in the head and must be forced out. Typical types of wear and the areas at which they occur are indicated for the rotor in FIG. 2 and for the hydraulic head in FIG. 3. In view of the fact that the operating clearances between the rotor and the hydraulic head must be maintained to millionths of an inch, even light scoring can cause leakage of an extent which will effect engine operation. Thus, in accordance with manufacturer's instructions "[a] ny component showing signs of threading, wear, damage, corrosion, cracks, or distortion, must be discarded."
Another comparable pump is the "ROOSA MASTER" Model DB of Stanadyne, Inc. Its instruction manual provides inspection instructions which indicate that "[i] f damage or excessive wear is apparent, the head and rotor must be replaced as a mated unit." The common locations for wear that can lead to seizing of such pumps and the causes therefor can be found in "ROOSA MASTER" service bulletin No. 203R1, January, 1965, for example. Similar circumstances exist with respect to the rotor and head of Bosch "VE" fuel injection pumps and many others as well. Likewise, inline distributor pumps, such as Bosch "A", "B", "K" and "Z" diesel injection pumps face similar types of damage and wear problems requiring replacement of the slotted and grooved, plunger and barrel distribution assembly found in such pumps. As a result, many millions of dollars worth of worn head and rotor assemblies, as well as plunger and barrel assemblies, must be discarded each year.
The large number of such discarded worn and/or damaged head and rotor or plunger and barrel distribution assemblies would represent a valuable resource if they could be salvaged. A salvage technique used, for example, with engines and other assemblies, where one or two coacting parts is much more expensive to replace than the other, and where extremely precise matching of parts is not as critical as in the case of the above-noted type of distributor fuel pump assemblies, is to machine the damaged wear surface of one of the parts (such as the piston cylinder holes of an engine block) so as to eliminate all wear defects, and then to replace the other worn component (such as the piston heads) with a corresponding part whose diameter deviates from that of the replaced part by an amount corresponding to the change in diameter of the machined part (i.e., in the case of an engine, an oversized piston head would be used in the machined-out cylinder space of the engine block). However, in the case of distributor pump rotor and head assemblies, or plunger and barrel assemblies, no such great disparity exists between the cost of the rotor and the head, or plunger and barrel, as in the engine block and piston example. Furthermore, because of the requirement for precision matching of, for example, the rotor and head, replacement rotors and heads are only available in precision matched sets.
On the other hand, since the rotor of one set may be larger than that of another and since the degree of wear experienced by one rotor head would be different from that experienced by another, a partial salvage technique is available only to those having large numbers of worn rotor and head assemblies. That is, by mixing and matching amongst the various discarded parts, it is possible to find rotors from some assemblies which, after machining, can be matched with remachined hydraulic head assemblies of other units. Such a technique may yield a salvage rate of, perhaps, 20% salvageable parts from amongst a large number of discarded assemblies. However, since hundreds of thousands of such assemblies still must be discarded each year, even the existence of such a limited salvage technique leaves a great demand for a workable method for salvaging fuel pump head and rotor assemblies that have become so worn that they would otherwise have to be discarded.
Another technique used to decrease the number of parts which must be discarded because they have become unusable due to wear caused by dirt or friction is to increase the ability of the parts to resist wear in the first place. Thus, in patents such as U.S. Pat. Nos. 2,180,883 and 1,971,433, a liner of a hard or hardened material is welded or press fit onto cylindrical members of frictionally interengaging parts in order to increase their resistance to wear. Such wear resisting sleeves or liners have been used even in the fuel pump art, such as for the pistons of reciprocating piston pumps or the cylinders of such pumps. However, such sleeves have not been utilized in connection with rotors and hydraulic heads of distributor type fuel pumps because of the problems of securing such sleeves in place upon the rotor and/or hydraulic head with proper alignment between the various ports in the rotor and/or head with those of the corresponding sleeve. Likewise, the presence of the grooves and slots of plunger and barrel distribution assemblies have caused such techniques not to be used on in-line injection pumps, as well. Furthermore, the costs associated with such techniques would generally be considered impractically high, especially in light of the associated problems of use.
Similarly, numerous techniques for chromium plating cylindrical bearing surfaces have been used for the production of new engine block housings and piston sleeves (see, for example, U.S. Pat. Nos. 2,968,865; 3,171,189; 3,888,746; and 3,981,688) but, such techniques have not found use in the pump arts, nor are applicants aware of their having been used in the salvaging of worn parts, presumably for cost and/or feasibility reasons.